1. Field of the Invention
The present invention relates to a control apparatus for an automatic lathe, which is used for successively choosing a plurality of tools one by one and machining a workpiece into a desirable form according to a machining program.
2. Related Background Art
With reference to FIGS. 13 and 14, the configuration of a conventional automatic lathe, e.g., Swiss type automatic lathe, will be explained. In an automatic lathe L, a workpiece 100 is driven to rotate in the direction of arrow A about a center axis of rotation J, while being movable in the directions of arrow B. An area slightly wider than the outside diameter d of the workpiece 100 is defined as a machining area D. Tools move within the machining area D at a predetermined machining speed, thereby machining the workpiece 100. A plurality of tools 101, 102 are disposed perpendicular to the center axis of rotation J. According to machining instructions, the tools 101, 102 move in the directions of arrows E, F, respectively, from their retracted positions indicated by solid lines in FIG. 13.
The tools 101, 102 are rapidly fed until they reach the machining area D (until they reach their respective positions indicated by dash-double-dot lines from the positions indicated by solid lines in FIG. 13), since they are unrelated to the machining of the workpiece 100 until then. The rapid feeding speed has been set for each of the tools 101, 102 by a machining program beforehand. The starting timing for rapid feeding is set in the machining program as well. Also, as shown in FIG. 14, a tool 103 is disposed near the tool 101. As with the tools 101, 102, the tool 103 moves from its retracted position according to a machining instruction. The tool 103 is rapidly fed until it reaches the machining area D.
As shown in FIG. 14, the tool 101 is held by a tool holder 104. Similarly, the tools 102, 103 are held by tool holders 105, 106, respectively. The tool holders 104, 105, 106 move together with their corresponding tools 101, 102, 103.
Now, with reference to FIG. 15, a control apparatus for an automatic lathe in a conventional technique will be explained. A control apparatus 110 for the automatic lathe L includes a numerical controller NC. The control apparatus 110 comprises an input device 111 for inputting a machining program expressed by a predetermined language, a readout section 112 for reading out the machining program from the input device 111 and digitizing it, and a machining program storage section 114 for storing the digitized machining program into a timing table form in the order of execution.
Here, an example of mode of storage in a timing table form in the machining program storage section 114 will be explained with reference to FIG. 16. The machining program storage section 114 memorizes that the tool 101 is located at its retracted position P0 at the point of timing to indicated by time, is placed at its machining operation starting position P1 at the point of timing t1 and maintained there until the point of timing T1, and is located at a position P2 within the machining area D at the point of timing T2.
An interference determining section 113 is connected to the readout section 112. The interference determining section 113 determines whether the inputted machining program is appropriate or not, and further determines whether interference occurs or not among individual movable parts of mechanisms in the automatic lathe when the machining proceeds according to the machining program. The result of determination in the interference determining section 113 is fed back to the input device 111. Here, data concerning the machining program determined by the interference determining section 113 to generate no interference are stored into the machining program storage section 114.
The machining program storage section 114 sends out the positional data of tools 101, 102, 103 stated in the stored machining program, rotational data and movement data of the workpiece 100, and the like to an instruction generator 115 according to the order of proceeding of program.
The instruction generator 115 converts thus received positional data of tools 101, 102, 103, rotational data and movement data of the workpiece 100, and the like into control signals of their corresponding motors. While receiving reference timing signals from a reference timing generator 116 which designates actual driving timings, the instruction generator 115 sends out the control signals to a control circuit 117 in synchronization with the proceeding of reference timing signals. An example of the control signals is a driving pulse signal for a predetermined motor.
While receiving feedback signals from a spindle rotating motor 119, the control circuit 117 functions to correct deviations from the inputted control signals such as driving pulse signals and outputs driving signals to a driving circuit 118. The spindle rotating motor 119 drives the workpiece 100 to rotate. Here, feedback signals from a spindle moving motor 120 for moving the workpiece 100 in the directions of arrow B, a first tool moving motor 121 for controlling the advancement and retraction of tool 101, a second tool moving motor 122 for controlling the advancement and retraction of tool 102, and a third tool moving motor 123 for controlling the advancement and retraction of tool 103 may be fed into the control circuit 117, the driving circuit 118, and the like.
The driving circuit 118 controls exciting currents to the spindle rotating motor 119, spindle moving motor 120, first tool moving motor 121, second tool moving motor 122, and third tool driving motor 123, and so forth, thereby actually driving the individual motors 119, 120, 121, 122, 123.
Now, with reference to FIGS. 17 to 24, machining processes by thus configured automatic lathe L will be explained.
First, FIG. 17 shows a xe2x80x9ccutting-off processxe2x80x9d in which the tool 102 severs an article 107 from the workpiece 100. The tool 102 moves at a predetermined machining speed in the direction of arrow F11 from the machining operation starting position indicated by dash-double-dot lines. The tool 101 is located at the retracted position P0 (see FIG. 13 or 14). Then, as shown in FIG. 18, the tool 102 moves in the direction of arrow F12, whereby the article 107 is completely cut off. Here, the tool 101 is still located at the retracted position P0 without moving.
FIG. 19 shows a state where initial positioning for carrying out the subsequent machining process is effected. The tool 102 moves in the direction of arrow F13, so as to be positioned at the edge of machining area D. The tool 101 to be involved with the subsequent machining process moves at a rapid feeding speed in the direction of arrow E11, so as to be positioned at the edge P1 of machining area D (see FIG. 13 or 14). The workpiece 100 moves in the direction of arrow B11, to a position indicated by a solid line. The completion of such initial positioning is governed by the most time-consuming one, whereas those having arrived earlier would wait at their reached positions.
FIG. 20 shows a state immediately before starting a xe2x80x9crough-cutting processxe2x80x9d by the tool 101. The tool 101 moves in the direction of arrow E12, thereby reaching a position immediately before starting an actual machining operation. The workpiece 100 moves in the direction of arrow B12, thereby reaching a position immediately before starting the actual machining operation. FIG. 21 shows a state where the xe2x80x9crough-cutting processxe2x80x9d by the tool 101 is completed. The workpiece 100 moves in the direction of arrow B13 thereby reaching its actual machining operation ending position. The tool 101 moves in the direction of arrow E13 according to the machining program as the time passes.
FIG. 22 shows a state where initial positioning for carrying out the subsequent xe2x80x9cfinishing processxe2x80x9d by the tool 103 is effected. The tool 103 moves at a rapid feeding speed in the direction of arrow G11, thereby reaching the edge of machining area D. The workpiece 100 moves in the direction of arrow B14, to a position indicated by a solid line. The tool 101 returns in the direction of arrow E14 at a predetermined cutting speed within the machining area D and at a rapid feeding speed when letting out of the machining area D.
FIG. 23 shows a state immediately before starting the xe2x80x9cfinishing processxe2x80x9d by the tool 103. The tool 103 moves in the direction of arrow G12, thereby reaching a position immediately before starting the actual machining operation. The workpiece 100 moves in the direction of arrow B15, thereby reaching a position immediately before starting the actual machining operation.
Finally, FIG. 24 shows a state where the xe2x80x9cfinishing processxe2x80x9d by the tool 103 is completed. The workpiece 100 moves in the direction of arrow B16, thereby reaching its actual machining operation ending position. The tool 103 moves in the direction of arrow G13 according to the machining program as the time passes. The tool 102 waits at the edge of machining area D (state shown in FIG. 19). Thereafter, the tool 103 returns to the most retracted position in order to keep it from interfering with the tool 101, whereas the machining process can return to the xe2x80x9ccutting-off processxe2x80x9d by the tool 102 shown in FIG. 17.
As explained above, according to the machining program, tools instructed to be chosen in a conventional common control apparatus for automatic lathes are moved to their machining operation starting positions and are kept waiting there until a timing for starting a machining operation, at which they are caused to carry out the machining operation. The movement of tools to their positions for starting the machining operation is carried out at a rapid feeding speed instructed beforehand by the machining program. This is done in order to shorten the time required for moving the tools not involved with the actual machining.
In such a method, however, a difference in amount of abrasion occurs due to the difference in speed between parts used with rapid feeding operations and those used with machining operations in a tool moving mechanism such as a ball screw for moving a tool. The parts used with rapid feeding operations may yield a remarkably greater amount of abrasion. Therefore, as the operating time of tool moving mechanism is longer, the tool feeding is more likely to rattle near places where machining starts. Also, as the rapid feeding speed is higher, the residual vibration upon stopping is more likely to continue for a long time, and the vibration is further accelerated when the rattling exists. These lower the machining accuracy in the workpiece by tools.
In view of the foregoing, it is an object of the present invention to provide a control apparatus for an automatic lathe, which can restrain the machining accuracy of a workpiece from deteriorating, without increasing the machining time for the workpiece.
The present invention provides a control apparatus for an automatic lathe for successively choosing a plurality of tools one by one and machining a workpiece into a desirable form according to a machining program; the control apparatus comprising storage means for storing the machining program, editing means for editing movement data of the tools according to the machining program stored in the storage means, and control means for controlling a moving operation of the tools according to the movement data edited by the editing means; wherein the machining program includes at least a program for instructing a first machining process by a first tool and a program for instructing a second machining process by a second tool carried out subsequently to the first machining process; wherein the editing means determines a movement starting timing of the second tool such that at least the second tool reaches a machining operation starting position at a machining operation timing instructed by the machining program and at a predetermined speed lower than a speed instructed by the machining program, when the workpiece and the second tool are caused to reach respective machining operation starting positions in the second machining process after the first machining process is completed, and the editing means defines the movement starting timing and the predetermined speed as the movement data.
In the control apparatus for an automatic lathe in accordance with the present invention, when the chosen second tool is moved so as to reach its machining operation starting position between the first and second machining processes, the editing means changes the moving speed of second tool to a predetermined speed lower than the speed instructed beforehand by the machining program. As a consequence, abrasion is reduced in parts used with rapid feeding operations in tool moving mechanisms. Therefore, the residual vibration of second tool decreases when a rapid feeding operation switches to a machining operation near the machining operation starting position, whereby the operation of second tool is stabilized near the machining operation starting position. As a result of these, the machining accuracy of the workpiece can be restrained from deteriorating. Here, since the editing means determines the movement starting timing of second tool such that at least the second tool reaches the machining operation starting position at a machining operation timing instructed by the machining program and at a predetermined speed lower than a speed instructed by the machining program, the machining time required for machining the workpiece into a desirable form is restrained from increasing.
In the control apparatus in accordance with the present invention, the predetermined speed defined by the editing means may be a machining moving speed of the second tool from the machining operation starting position in the second machining process instructed by the machining program. As a consequence, the moving speed of second tool to the machining operation starting position thereof can be determined easily in a simple manner. Also, since the second tool reaches the machining operation starting position at the machining moving speed and enters the machining area to carry out the second machining process at the same speed, the operation of second tool becomes more stable, whereby the machining accuracy can further be improved.
In the control apparatus in accordance with the present invention, the editing means may determine whether the second tool interferes with the workpiece and the first tool or not after the second tool is started to move at the movement starting timing until the second tool reaches the machining operation starting position, and define the movement starting timing and the predetermined speed as the movement data when it is determined not. As a consequence, the second tool can securely be prevented from interfering with the workpiece and the first tool.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings. They are given by way of illustration only, and thus should not be considered limitative of the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it is clear that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, and various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.